Abstract

Debate continues about the environment of Antarctica during intervals in the Pliocene (5.2-1.8 Ma), particularly during the Late Pliocene(3.5-1.8 Ma). Two schools of thought - dynamic versus stable ice sheet - have developed. One hypothesis calls for the Antarctic icesheet to vary dramatically, for Antarctica at times to be vegetated and for circum-antarctic waters to be significandywarmer than at present.The other calls for a stable ice sheet, no vegetation and water temperatures much less varied. During 1995, the two sides converged byrecognising that the change to conditions suitable for vegetation may not have been as marked as originally thought, and that oxygenisotope data may contain scope for more flexibility in interpretation than the stabilist view has supported. New data and new participantshave emerged, but there is a long way to go in resolving the issue.The key issue remains the age of the Sirius Group in the Transantarctic Mountains and the source of its contained diatoms. Diatomsof Pliocene age have been recovered from the Sirius Group but also from modern ice, and this raises the question of whether the SiriusGroup diatoms are actually in situ.New data and re-evaluation of existing data are necessary. Ocean Drilling Program activity, particularly in the Prydz Bay region, andanalysis of samples from the Prince Charles Mountains can be expected to contribute significantly to a solution, by providing moreinformation on past temperatures and evidence of possible terrestrial vegetation.